It is not easy to follow orangutans through the forest. They swing through the trees with the greatest of ease, forcing the poor lumbering biped to push through brush or wade through swamps, risking life-threatening encounters with insects, snakes, crocodiles and more, to keep up.
But this was the life that the young primatologist Biruté Galdikas, who has died aged 79, chose in 1971, and in the decades that followed she added the third and fourth dimensions to the very flat image of these critically endangered animals that scientists had held until then.
Her patient observation of the “people of the forest” – the English translation of the Malay expression orangutan – revealed that they have the longest birth interval of any land mammal, with a female producing an infant every seven or eight years and investing herself intensively in its rearing. She showed that although orangutans were omnivores, fruit constituted the major part of their diet.
They acted as the “gardeners of the forest”, being the only animal big enough to distribute the seeds of the larger plants, through the simple act of digestion. By breaking the occasional branch in the canopy they also let in the light, encouraging regrowth. Nor were they strictly solitary, as had been thought. The males were, though even they occasionally came down from the canopy to lope across the forest floor, but the females lived in loose matrilineal groups – a pattern found across the great apes.
Following Galdikas’s pioneering example, other fieldworkers would observe orangutans using tools – something that Jane Goodall had reported earlier in chimpanzees, and that had previously been considered exclusively human. They showed that the orangutans’ choice of tools and the tasks for which they used them varied across populations, which was evidence of culture.
The picture that Galdikas and those who came after her built, of a species whose survival depended on the transmission of information across groups and generations, went a long way towards explaining why orangutans are so vulnerable to threats to their environment – and why their declining population numbers have occasionally tipped into freefall.
It was natural, then, that Galdikas should become preoccupied with conservation early in her career. In this she followed her friends, Goodall, who died last year, and the mountain gorilla expert Dian Fossey, who was murdered in Rwanda in 1985. Photos of the “trimates”, as the three women were affectionately dubbed, cuddling orphaned apes or leading them by the hand graced many a magazine cover, until they triggered a backlash.
Galdikas, in particular, was criticised for her work as a surrogate mother to hundreds of orphaned orangutans. The infants she reared behaved differently from their wild counterparts by the time they were released, the critics said, and she was altogether too close to them. This not only affected her objectivity, they claimed, but it also increased the risk of interspecies disease transmission.
Gillian Forrester, who researches ape cognition at the University of Sussex, defended the trimates. Disease risk was less well understood in their day, she said, and although the methods of rehabilitation have evolved in light of new knowledge, human surrogate mothers are still often the only option for orangutan orphans that would normally spend their first seven years inseparable from their real mothers. “Those women worked in an age of discovery,” Forrester said. “Now we’re moving into an age of responsibility.”
The criticisms should not detract from the women’s remarkable achievement, she maintained, which was to add the female perspective to our understanding of our closest relatives, and in so doing to narrow the illusory perceptual gap between humans and the other apes. They did so by asking questions that male primatologists had not thought to ask – about the role of female choice in shaping social hierarchies, for example, or about gender-based decision-making day-to-day. By revealing the remarkable strength of these animals’ social bonds, their individual characters and the depth of emotion of which they were capable, the trimates portrayed them as more human-like than science had previously allowed.
Biruté was born in Wiesbaden, Germany, to Antanas Gildakas, a house painter, and his wife Filomena (nee Slapsis), who worked as a nurse. Her parents, who were both of Lithuanian origin, eventually moved the family – Biruté, and her two brothers and a sister – to Toronto, Canada, where Biruté nurtured a fascination for human evolution.
That fascination would crystallise around orangutans – the only great ape found in Asia – because they were thought not to have evolved very far from their ancestral state, and because of their eyes. “Their eyes have whites around the iris … just like humans,” Galdikas told an interviewer in 2011, on the release of a film about her work, Born to Be Wild.
As a student at the University of California, Los Angeles, she encountered the palaeoanthropologist Louis Leakey, who encouraged her and her fellow trimates to undertake fieldwork – the reason they became known, alternatively, as “Leakey’s angels”.
In 1971 Galdikas created her first camp in central Borneo, with her then husband, the photographer Rod Brindamour, whom she had married the previous year. “The swamps, swollen by rain, were waist deep and impassable,” she told National Geographic four years later, about arriving at the site they would name Camp Leakey in her mentor’s honour. “Leeches were everywhere. Bloated with our blood, they fell out of our socks, dropped off our necks, and even squirmed out of our underwear.”
It was a foretaste of the life to come, embedded in the forest, living at the rhythm of the orangutans – being alert from the moment they left their nest, typically before 6am, to the moment they built a new one at dusk. She had to be there all day every day for years, so that the animals accepted her presence and she could discern patterns in their behaviour – the reason, perhaps, that when she and Brindamour divorced in 1979 they agreed that he should have custody of their young son, Binti.
It was physically demanding, lonely work, but Galdikas wanted no other. Meeting her at a wildlife film festival in New York City in 2014, at which they were both being honoured, the US primatologist Mireya Mayor recalled: “She seemed like someone who had stepped out of the forest temporarily … her heart and mind were still there.”
Galdikas understood that outreach was essential to conservation, as was the involvement of local people. The organisation that she created in 1986, Orangutan Foundation International, will continue to be run by an Indonesian team headed by Frederick, her son with her second husband, Pak Bohap, a native Bornean, whom she married in 1981. The foundation has contributed to the release of more than 1,000 rehabilitated captive orangutans into the wild, and rescued and relocated another 200 wild orangutans.
When she talked about her work, Galdikas did not shy away from the dangers she faced. The greatest threat to the animals’ habitat came from loggers and palm oil plantation owners. She received death threats and was once kidnapped. “I was struggling against an industry that was making billons of dollars,” she said in an interview last year. “It did sometimes come to physical violence.”
She nearly died of malaria too, but in the end, arguably, it was the forest that claimed her. She was diagnosed with lung cancer and pulmonary fibrosis, two conditions exacerbated – in the view of those close to her – by her efforts to contain wildfires in her beloved Borneo.
Bohap died in 2022. Galdikas is survived by her children, Binti, from her first marriage; Frederick and Jane, from the second; and seven grandchildren, and her sister, Aldona.
• Biruté Mary Galdikas, primatologist, born 10 May 1946; died 24 March 2026
